Overview
Hopefully, you all got some rain last weekend. It was light in Tucson and, as in the folklore, it missed both the Phoenix and Tucson airports with only a trace recorded at each location. The 48-hour accumulated MRMS observations (Sat-Sun) below show the White Mountains and the peaks in Gila and Coconino counties fared a little better with rainfall accumulation between 0.5 and 1.5”. Humphreys Peak (11,500ft) is reporting 9” of snow depth already, and Sunrise Peak (10,700ft) got a dusting.
This week, the train of low-pressure systems continues with another system impacting the region, bringing more wet weather today into tonight and tomorrow for Arizona and New Mexico.
Current conditions
The mid-level water vapor satellite loop from midnight to 9am this morning shows an elongated trough stretching from southern Nevada, through southern California, then well into the Baja Peninsula. Moisture is being advected from the southwest in two bands; one over western Arizona moving north, and one over New Mexico moving north east. Currently there’s a dry slot separating them.
Analysis
From today into tonight, the low-pressure system will move west before breaking up tomorrow afternoon over New Mexico. Ahead of its path, we are in a broad area of positive vorticity advection, which will generate the synoptic-scale vertical lift required to create thunderstorms/showers, as shown in the 500mb forecast below.
The two bands of moisture advection mentioned earlier will converge as the trough is squeezed northward. The 300-700mb integrated water vapor transport forecast below shows the up to 60kt jet of moisture coming from Mexico into New Mexico and west Texas.
Today and Tomorrow
The forecast skew-Ts for Phoenix at 4pm (left) and Tucson at 9pm (right) show better chances for thunderstorm development in Phoenix with over 450 [J/kg] of Convective Available Potential Energy (CAPE). Though vertical motion is still forecast for Tucson skew-T, as shown by the negative Omega values on the top right red bars, as a result of the synoptic lift described earlier.
The simulated radar reflectivity shows widespread activity starting in western Arizona today. Phoenix already got 0.15” at the airport and another round is predicted for this afternoon (around 4pm). New Mexico has activity throughout the day and by nightfall the convergence of the moisture advection will mean Tucson gets it’s chance. Storm cells could start around 6pm and rainfall is expected from around 9-10pm into the early morning and sunrise.
Accumulation of 0.25” to 0.5” are predicted for Tucson across the four morning UA WRF forecasts. Snow accumulation is restricted to the higher elevations on the Mogollon Rim and into western New Mexico, shown on the right.
Here’s the UA WRF ensemble plume forecast for Tucson; the ensemble mean predicts 0.4” through tomorrow afternoon.
Outlook for the weekend
The weather should calm down for the remainder of Thursday and Friday, as the low-pressure system weakens over New Mexico. Though the train keeps a-rolling, as a another low-pressure is on the way for the weekend.
The forecast radar reflectivity for Saturday morning shows another 0.25” for Tucson. Good luck to those participating in the El Tour de Tucson cycling event! Hopefully, the forecast changes for you, but at least if it does rain, it should be light.
Discussion written by Patrick Bunn